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Microsoft enlisted pop star Usher to launch a recent Xbox game but most actors who star in blockbuster titles remain unknown

It's 32 years since a video game was first blessed with the power of speech.

1980's Stratovox, a relatively poor hybrid of Space Invaders and Galaga, featured precisely three phrases from its human characters: "Help Me", "Very Good" and "We'll Be Back".

They sounded like a Dalek, in a tin bucket, broadcasting on long-wave radio during an electrical storm.

These days, the acting in video games has come on leaps and bounds. The biggest-budget titles use the same motion-capture technology as Hollywood films like Lord Of The Rings and Avatar to scan human performances and replicate them on screen.

Big franchises like Uncharted, The Sims, Far Cry, Mario Kart and Call Of Duty make their way into hundreds of millions of homes. If the actors were working in any other medium, they would be household names.

We spoke to three of the industry's most in-demand performers to find out how they started, and what it feels like to be a pixelated pin-up.

Charles Martinet

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The Mario series has taken Charles around the world

For the last 22 years, Charles Martinet has been the voice of moustachioed Italian plumber Mario, aka Super Mario.

It's a long way from his intended career in international law.

Martinet studied politics at the University of California, Berkeley, and was in his final year when he became disillusioned by a tutor, who demanded he "regurgitate information he'd written in his book, chapter-by-chapter".

"I couldn't do it, so I left," says the ebullient 57-year-old.

A friend persuaded him to take an acting class, forcing him to confront a fear of public speaking.

"My first monologue was as a dead person, coming back to tell the audience about the misery and horror of my death," he recalls.

"My right knee was bouncing up and down, so I put all my weight on that knee and all of a sudden my left knee was shaking up and down.

"Then both of my legs were shaking, and my teeth were clattering. But somehow I got through my ultimate terror in life.

"And people said, 'that was great, you were the only person who wasn't nervous!'"

Bitten by the bug, he went on to work in theatre and television, before branching out into corporate videos - "more than 600 of them" in total.

In 1990, he was sitting on a beach in California when a friend phoned to tell him about a nearby audition for a trade show.

The producer was looking for someone to provide a voice for Mario (who up to now had been mute) at a gaming conference.

Martinet would speak with dozens of electrodes "glued to my face", and a real-time animation system would make it seem like the words were coming from the character's lips on a nearby screen.

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Martinet still "plays" the character of Mario at trade shows, department stores and promotional events

"He told me I was an Italian plumber from Brooklyn," says Martinet, "so my instinct was to try a gruff and coarse voice - 'hey you, get outta my face!'"

But at the last minute, the actor decided to try a different tack. A Shakespearean tack.

"What popped into my brain was a character I'd played in Taming Of The Shrew," says Martinet. "I was Petruchio going back to get his wife in Italy, and I was a sort of 'Mamma mia, nice ol' Italian guy'. So I thought I'd do something like that.

"I went on and on about spaghetti and meatballs. After half an hour the producer said, 'cut, stop, we've run out of tape!'"

"And he called Nintendo and said 'I've found our Mario'. Mine was the only tape he sent back."

Martinet appeared at trade shows for six years using the face-tracking device. Every time he saw Mario's creator, Shigeru Miyamoto, walking past the booth, he would cry "papa!"

"Eventually, Nintendo called me up and said, 'Mr Miyamoto would like you to play the voice of Mario in a new game', which was Mario 64.'"

Martinet's high-pitched, cartoonish voice has graced more than three dozen Mario games since then.

The plumber always speaks English, Martinet points out, "although sometimes we do a slightly different version for Japan".

"It's such a profound honour," he says.

"When I was in London for the launch of Mario Galaxy, this wonderful young man approached me and said - and I quote: 'Mel Blanc [Bugs Bunny] was the voice of my father's generation, you are the voice of mine.'"

Nicki Rapp

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Voice-overs are recorded in a similar way to cartoon characters

"When I was in school, teachers told me I was limited," says Nicki Rapp in an exuberant, helium-high squeak.

"They said I couldn't do theatre because of my voice. What I found with voice acting is I'm not limited at all."

Over the past 13 years, Rapp has played characters as varied as Morgan LeFlay, a swashbuckling pirate-hunter who can hold her breath for five minutes, in Tales of Monkey Island; and Lily, a survivor of the zombie apocalypse, in episodic drama The Walking Dead.

But in her biggest hit, she talks utter nonsense.

Rapp is one of the stars of The Sims, speaking the invented, but highly-realistic language, of Simlish (goodbye becomes "sul sul"). The series has sold more than 150 million copies worldwide.

Rapp records The Sims just down the road from her house in Oakland, California - "right across the bay from foggy San Francisco".

"There's a little countdown and the animation comes up," she explains of the recording process. "It could be a child doing any sort of activity - baking a cake, having a tantrum, building a snowman.

"Initially, I always improvised it, although now they have a little bit more of a script. But I am just a big nerd. I make up words a lot. I have a little notebook here and I write them down.

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Rapp voices several of the child characters in global smash hit The Sims

"I worked in a cafe in a hostel for about six years, and I met people from all around the world, so I'd use their names as Simlish, too."

Rapp says she was a "really shy" child who was pushed into acting classes to "bring her out of her shell". It worked. She's a chirpy, effervescent chatterbox with a perennially sunny disposition.

Her first acting job was on a "Nerf Junior CD ROM game", and her naturally-childlike tones have been used to bring numerous toys and dolls to life.

"I have a pretty good dog bark, and I've booked a few jobs doing that, too," she laughs.

Her character on The Walking Dead, based on the same comic strip as the hit TV series, has been "a big change", allowing her to grow up and flex her dramatic muscles.

"It's definitely the most intense acting challenge I've had," she says. "Lily is so different to me as a person. She can't show her vulnerability. Her father's a military man and she has this really hard edge to her."

Recording sessions last around four hours but, unlike traditional acting roles, Rapp lays down dozens of lines of dialogue that may or may not be heard, depending on the player's choices.

"A lot of the time, there's not really a flow in the recordings," she says. "They'll be like, 'ok this moment you're freaking out and screaming' and then they'll say, 'this is way back in the beginning when you were more innocent'. You really have to adjust yourself because nothing's really playing out in order.

The Walking Dead has just been commissioned for a second series but, despite her success, Rapp still isn't able to act full-time, working in a coffee shop in between jobs.

"I'm kind of ready to phase that out of my life," she says. "Customer service is rough.

"My ultimate goal is to be full-time, in a cartoon. I've got big dreams about this business."

Michael Mando

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Mando's performance for Far Cry 3 was motion-captured

Unlike Nicki and Charles, Michael Mando is instantly recognisable as Vaas - the philosophical, but psychopathic villain he plays in Far Cry 3.

The Canadian actor's performance was captured in a virtual 3D studio. His movements and facial expressions are recreated perfectly in the forthcoming game, a "shooter" set on a remote tropical island.

Mando says he had to draw on his experiences in both film and theatre to adapt to the new medium.

"It's all done in one take, like the theatre," he explains. "In film, I can say a line, another actor can say a line, and then it will cut back to me in a different take. In motion capture, there are no cuts.

"But the intimacy of the voice performance is at a film level. I can speak to you in my regular tone of voice, and it's loud enough, it's true enough, and it's honest enough."

Born in Quebec City, Mando says he got into acting "by accident".

Ten years ago, he was visiting his mother in Ivory Coast, West Africa, when he "got into a very big bar fight", which resulted in him being shot in the knee.

He had to give up his scholarship at the University of Montreal, and enrolled in a "very cheap theatre programme that cost about $100 (£63), because I didn't feel like getting a job".

"I had teachers who believed in me from the beginning," he says, "and I was offered work very early on".

Starting in theatre, he struggled to make ends meet - "I was working my butt off, but I did my own make-up and had to buy my own food" - until he won his first television contract.

"I was a stunt actor and I had maybe one line, which was then re-dubbed by another actor because they thought my acting was bad.

"But I got ten grand, and they gave me food for free, they gave me a small trailer, they drove me from my house to my set. I couldn't believe that I was so insignificant, but I was being treated this way and making this much money."

Appearances in TV series such as The Bridge and The Border followed, and Mando set up his own company, Red Barlo Productions.

The call to audition for Far Cry came out of the blue. Mando, who was "going through a very difficult emotional thing with a girl", says he accepted the invitation without much thought.

"I read the monologue. I thought it was really good, but the character I was going in for had nothing to do with me, so I decided to go in and give them something very different.

"I improvised a lot... [and] they decided to create a character based on the audition that I had done."

The actor confesses he hasn't played games since his childhood - "I have to be honest, the buttons got so complicated" - but he's impressed at how the technology has moved on.

"I've seen trailers for Far Cry 3, and I was blown away," he says. "It's really exceptionally entertaining."

And how do other actors feel about employment in video games?

"I just worked with Christopher Mintze-Plasse, who played McLovin in Superbad, and there's a curiosity about it.

"The general perception, is 'you're a video game character, that's really cool'. I don't think there's any snobbery about it at all."